1. Field of the Invention
The present invention relates to a method for operating an atomization nozzle.
2. Discussion of Background
During pressure atomization of a liquid fuel in a nozzle which is placed upstream of a combustion space, for example a combustion chamber of a gas turbine or an atmospheric firing system, irregularities in the atomization characteristic of the nozzle regularly occur in the course of an operating period, said irregularities having a negative effect in terms of efficiency on the subsequent burning of the fuel. One irregularity can occur due to wear of the nozzle and can have the effect that the spray angle no longer operates in an optimum fashion. Another irregularity can be caused by the fact that the nominal pressure of the fuel supplied fluctuates inordinately, resulting in an expansion and contraction of the spray angle. In addition, the nozzles on the market produce an excessively large spray angle, of the order of 40.degree.-50.degree., which is clearly at least 100% too much. Furthermore, such a nozzle operates very much as a function of the load range. If such a nozzle is then used in the atomization zone of a firing system with the ultimate end of providing a fuel/air mixture, this results in additional interference with the quality of atomization already attributable, for example, to pressure fluctuations of the air flow fed in. In addition, account must be taken of the fact that an air-assisted nozzle only functions at a pressure of 0.2 bar and above and that the air content in relation to the fuel is very high. An irregularity of the spray angle can in addition have a very negative effect in various firing units, whenever, for example, the atomization of the fuel is performed in a relatively narrow feed line leading to the firing space, as is often the case in premix burners. With such a geometrical configuration, an irregular spray angle can wet the inner walls of the premixing tube, where, in the case of a liquid fuel, relatively large fuel droplets rapidly form. If these are then taken along by the air flow, an inhomogeneous mixture reaches the firing space for combustion, leading to a poor firing characteristic. Not only is this noticeable in terms of poor efficiency, it also has a negative effect on pollutant emissions, such that it rapidly becomes impossible to comply with the legally prescribed maximum values. A further problem in this connection also arises when firing systems are to be operated whose air pressure is virtually non-existent, as is the case, for example, with atmospheric firing systems. In such cases, the prior art, i.e. the air-assisted nozzles which have been disclosed, are incapable of offering a satisfactory solution since an increase in the pressure of the air would here have to be specially produced, this having negative consequences for the costs and the efficiency of this same firing system.